LCD-TV repair

[PowerAmpFreak]

Re: LCD-TV repair

How is the sequence of changing a CCFL tube?
By the way, I assume there are several tubes to fill the entire screen, so could one tube fail and the other operate? Or does a faulty tube take the other out as well, because they are parallell connected?

[PlainBill]

Re: LCD-TV repair

This inverter design uses two transformers on the same board. Each transformer has one single output. Each output is connected to the panel.
Plainbill, how do you verify the level of high voltage? Do you have a high voltage probe?
Is lamp failure a common problem, really?
I don't know what it could be else, if the inverter provide proper HV.

The only high voltage probe I have was designed to check the high voltage on CRTs. I doubt it would be accurate on the output of an inverter.

I know nothing about the design of the balancer circuits, but I would think if a single CCFL failed there would either be some sort of error indication or the rest of the lamps would continue working.

PlainBill

[PowerAmpFreak]

Re: LCD-TV repair

What I have verified so far, is that inverter starts and runs for two seconds, then shuts off. This must be due to a protection circuit that senses some abnormality. It might be the CCFL current draw which is out of limits.
I would need a way to verify the status of the CCFL, obviously.

[Tvbob]

Re: LCD-TV repair

Bud,65 ohms is way to low. Google the number on the inverter transformer to find more info on it. there are a couple good sites on net that sell transformers. (ebay)

[f67bird]

Re: LCD-TV repair

How is the sequence of changing a CCFL tube?
By the way, I assume there are several tubes to fill the entire screen, so could one tube fail and the other operate? Or does a faulty tube take the other out as well, because they are parallell connected?

Most or all of the tv inverters drive each tube individually and have a circuit that detects too much or too little current being drawn in each tube. If one or more tube fails or starts drawing too much current, the inverter will usually completly shut down all tubes.

Changing one or more tubes would involve taking the panel completly apart and will vary from set to set.
More common are faults in the inverter itself... which can cause the same symptom.

[alexanna]

Re: LCD-TV repair

^
I have read about some LCD TVs that will throw a code for a CCFL out. And continue to light the CCFLs for viewing.
In any case if you suspect a CCFL problem why not substitute a known good Bulb?
CCFLwarehouse dose give strike/run voltage,Amprage Ect. On some of the longer CCFLs

[PowerAmpFreak]

Re: LCD-TV repair

Bud,65 ohms is way to low. Google the number on the inverter transformer to find more info on it. there are a couple good sites on net that sell transformers. (ebay)

Thanks Bob, I will investigate the transformers and check why the secondary measures only 65 ohms. Please note that I got this reading by measuring right across the two high voltage output wires. Measuring only across the CCFL, reads infinite, as it should.

[PowerAmpFreak]

Re: LCD-TV repair

The inverter seen in first picture has an external, what it seems, a light detector mounted on the panel. This must be to verify that CCFL comes on or not. In my case, not. I was brave enough to hook up my HV-probe directly on the HV output and could verify something around 2-2.5kV peak which I assume is correct. Still the CCFL won't start.
I took the TV completely apart, trying to get into the source of the problem. But it looks like the panel is built as a module (third picture) and won't be possible to split, so I cannot get in touch with the CCFL's. The panel partnumber is shown in the second picture.
So I guess this will be the end of this, since I cannot check the lamps, this TV will not be possible to repair.

[PlainBill]

Re: LCD-TV repair

While I'm sure that Samsung has decreed that "What Samsung has joined together let no man rend asunder", I'm of the opinion someone of sufficient skill can do so successfully. Perhaps close up pictures of the sides of this assembly would yield a clue.

PlainBill

[PowerAmpFreak]

Re: LCD-TV repair

What concerns me, and what tells me this is a "no-go" is that the housing that hides the CCFL has steel rivets which means I must drill all of them out. This will not be economically defendable in my opinion.
But for the sake of interest, this would be a thing to do a rainy day.
Will provide you with additional pictures in a few days.

[PlainBill]

Re: LCD-TV repair

What concerns me, and what tells me this is a "no-go" is that the housing that hides the CCFL has steel rivets which means I must drill all of them out. This will not be economically defendable in my opinion.
But for the sake of interest, this would be a thing to do a rainy day.
Will provide you with additional pictures in a few days.

They sealed it with rivets? That is a dastardly act!

PlainBill

[alexanna]

Re: LCD-TV repair

They sealed it with rivets? That is a dastardly act!

PlainBill

Wasn't it rivets that broke on the Titanic?

[kc8adu]

Re: LCD-TV repair

i would not tear the panel down or give up yet.the ones with 2 leads are what are known as eefl.
the way those are used one could die and the others would still light.since by design each are capacitively coupled already they are simply connected in paralell.
look back at the inverter.

[PowerAmpFreak]

Re: LCD-TV repair

i would not tear the panel down or give up yet.the ones with 2 leads are what are known as eefl.
the way those are used one could die and the others would still light.since by design each are capacitively coupled already they are simply connected in paralell.
look back at the inverter.

I can't see any problem with the inverter. It generates high voltage and supplies this to the lamps, but the lamps doesn't come on.
During each power up, the inverter transformers are driven for 2 seconds, then shuts off. Since the lamps doesn't come on, the light detector is feedback to the inverter board, and shuts it off.
I agree with you, in a parallell design one failed lamp would not affect the other. I'm confused.

[alexanna]

Re: LCD-TV repair

I can't see any problem with the inverter. It generates high voltage and supplies this to the lamps, but the lamps doesn't come on.
During each power up, the inverter transformers are driven for 2 seconds, then shuts off. Since the lamps doesn't come on, the light detector is feedback to the inverter board, and shuts it off.
I agree with you, in a parallell design one failed lamp would not affect the other. I'm confused.

Have you thought about replacing the 35V 680UF capacitors on the inverter?

[PowerAmpFreak]

Re: LCD-TV repair

Have you thought about replacing the 35V 680UF capacitors on the inverter?

yes, thought - but never did. Since I saw no obvious sign of problem with them. Do you know this inverter board? Is this a known issue with it?
If this is the solution I'll be ashamed. ...and very very happy!

[alexanna]

Re: LCD-TV repair

I know of no issues,But at this point you have nothing to loose by trying them.Well maybe 4 bucks.

[PowerAmpFreak]

Re: LCD-TV repair

Will be the first thing to do when I see it again!

[PowerAmpFreak]

Re: LCD-TV repair

Have you thought about replacing the 35V 680UF capacitors on the inverter?

Said and done, no improvment after changing the 680uF caps. This one is nagging me. One question, does the CCFL or EEFL lamps turn on directly after supplying HV to them? Or could it take a few seconds?
Why I'm asking is that inverter starts up for one or two seconds, then shuts off. So I wonder if it during this short time has the ability to sense the light by the panel light detector, or if the reason for shut off is that it senses any abnormal current consumption by the lamps.
Or if the HV is out of range, low or high.

[PowerAmpFreak]

Re: LCD-TV repair

What about taking the light detector off the panel and let an external lamp "simulate" the panel lamps? This would mean the inverter shouldn't shut off due to backlight failure. Maybe this can give me a clue what's going on in there.